DESCRIPTION (adapted from the application) The goal of this application is to study the interactions of iron response proteins with their RNA binding sites, using X-ray crystallography. These interactions play a central role in the regulation of iron transport and homeostasis. Diseases of iron transport and metabolism are among the most prevalent causes of human suffering and mortality. A greater understanding of the regulation of iron absorption and utilization will be important in developing treatments for iron deficiency and iron overload. Iron regulatory proteins (IRPs) exert translational control over the levels of other proteins involved in iron metabolism. Two IRPs are known, IRP-1 and IRP-2. When iron levels are low, these proteins recognize specific stem/loop structures known as iron response elements (IREs), which are present in the target mRNAs. For proteins whose levels are downregulated in low iron, the IRE is typically found in the 5' untranslated region of the message and binding of the IRP to the IRE inhibits translation of the message. For proteins that need to be expressed at higher levels under low iron conditions, the IRE is generally found in the 3' untranslated region, where IRP binding stabilizes the transcript, resulting in increased expression of the protein. Using X-ray crystallography, we will pursue the structure of IRP-2 alone and in complex with the two known classes of IRE mRNA binding sites. We will pursue crystal structures of IRP-2 in complex with a C bulge type IRE, and in complex with a ferritin loop/bulge type IRE. Upon the completion of IRP-2 structures, further structure function studies will be initiated. These studies will use site directed mutagenesis, biochemical characterization and structure determination to further explore IRP-2/IRE structure and function. The greater insight provided by these studies into the specific interactions of IRPs with IREs may lead us a step closer towards the development of treatments for disease of iron metabolism.